Libyans celebrate the fall of Sirte and the death of Muammar Gaddafi. Photograph: Mohamed Messara/EPA

"Everyone can now draw a line. This is the final curtain. This is the beginning of a new chapter," declared Guma al-Gamaty after Gaddafi's death was confirmed.

The drawing of the line, predicted by the UK-based co-ordinator for Libya's National Transitional Council, will be made official when the head of the council, Mustafa Abdel Jalil, proclaims the formal liberation of Libya.

That should set in motion a long-planned chain of events, starting with the formation of an interim government that will run the country for about a year while overseeing preparations for elections.

Western diplomats involved in these plans said the interim government would include representation from across Libya, bringing together the various factions that brought about Gaddafi's downfall.

The acting prime minister, Mahmoud Jibril, reinforced the message of unity, declaring: "We confirm that all the evils plus Gaddafi have vanished from this beloved country. I think it's for the Libyans to realise that it's time to start a new Libya, a united Libya, one people, one future."

Most diplomats agreed on Thursday that Gaddafi's death would help stabilise the position of Libya's new leaders, particularly if his followers now gave up the fight.

Before the final shootout in Sirte, there were reports that Gaddafi was recruiting mercenaries from across Africa, paid with looted gold, for his fightback. The spectre of a drawn-out guerilla war loomed.

That threat has receded, although the possibility remains that Gaddafi's death might make him a martyr for armed diehards, who will not have been encouraged to hand themselves in by their leader's televised fate.

The bigger threat now is likely to be the prospect of splits among the victorious factions – the NTC leaders who first raised the banner of revolt in Benghazi at the start of the year, the Misrata militia who did much of the fighting, lost the most people and see themselves as the deserving "Spartans" of the new Libya, and the fighters from the Nafusa mountains in the west, who tipped the balance against Gaddafi in August.

The Misrata brigades, in particular, have used their military successes to arm themselves to the teeth, driving away tanks and artillery on huge lorries from every Gaddafi loyalist bastion they overran.

"I don't think there is any way there won't be a power struggle," said Rosemary Hollis, professor of Middle East policy studies at City University, London. "You have those who did the bulk of the fighting and lost lives and limbs, and those who did the necessary task of doing the diplomacy and so spent much of the time abroad, and those who have cropped up in the last week – those for whom capture or trial is an appalling prospect. There will be score settling."

Al-Gamaty, however, rejected predictions that the revolution would now devour itself in internecine conflict. He said such internal strife had been forecast for months, but had yet to materialise. "Our co-operation is going smoothly, and now things will be easier. We will be even more organised."

British diplomats say that, behind the scenes, the NTC has been making strenuous efforts to ensure the interim government will be inclusive and geographically representative, and has had concrete successes in restoring some services, such as getting the water flowing again in Tripoli.

Daniel Korski, who runs the Middle East programme at the European Council for Foreign Relations, said: "There are cleavages, but they are not as deep-rooted as so many others in other countries, and they are not as politically salient. You have not had the generations of bloodletting we have seen elsewhere. It's more Albania than Bosnia."

The celebrations surrounding Gaddafi's fall provide another unifying moment, but the departure of the one man who united much of the country in fear will pose fresh challenges. Libya's new rulers now have to find different reasons to stick together.